This invention relates to a programmable logic device (PLD) or field programmable gate array (FPGA). In particular, it relates to the implementation of a power source for the device.
A programmable logic device is an integrated circuit, which includes a large number of logic elements, usually arranged in the form of an array. After manufacture, these logic elements can be combined, by programming the possible interconnections between the logical elements in a particular way, so that the device performs a particular desired set of functions.
In order to allow the required interconnections to be made, the programmable logic device includes a routing structure. The routing structure allows communication between the different logic elements in the array.
After manufacture of the programmable logic device, functions are allocated to the logic elements, and the interconnections between the logic elements are programmed, in such a way that the device performs its intended overall function.
The data which causes the logic elements to perform the intended functions, and which causes the intended interconnections to be made, is referred to as ‘configuration data’, and is typically stored in a separate configuration memory device. Then, when power is first supplied to the device, the configuration data is loaded from the configuration memory into the device, which is then ready to perform its intended functions.
It is known in the field of integrated circuit design that the overall power consumption of a device can be reduced by removing power supplies from presently inactive parts of the device. When a part of an integrated circuit device is connected to its power supply, there will always be some current leakage, using conventional technologies, and hence some power consumption within that part of the device. This power consumption can be avoided by powering down the unused parts of the device.
There are many applications of integrated circuit devices, in which it is highly desirable to reduce the power consumption. For example, in the case of battery-powered devices, the available operating time of the device is determined directly by the power consumption. In other cases, a high power consumption requires that the equipment be provided with special heat dissipating elements, adversely affecting the size and cost of the equipment.
However, simply powering down a programmable logic device has the serious disadvantage that, when the device is next required to be functional, it is necessary to perform a potentially lengthy configuration sequence, before the device becomes operational once more.